In flat joint explosion proof enclosures it is necessary that the mating surfaces be machined to close tolerances so that the surfaces are in intimate contact. Often these enclosures are of cast metal and quite heavy and the cover is hinged and swings outward. The screws which hold the cover to the enclosure body when the cover is closed can scratch the mating surfaces and lead to failure of the flame tight boundary if protruding below the surface of the cover when the cover is swung closed.
Prior art attempts to solve this problem have involve the use of friction type sleeves, so that after the screw was disengaged it could be pulled out to a stop and held in place in a retracted position. The disadvantage of this arrangement was that the operator may forget to retract all the screws and therefore the flame surface would be damaged.